This invention relates generally to detonator apparatus, and, more particularly, to detonator apparatus for actuation underground in a borehole, usually by means of a line mechanically attached to the apparatus.
For a variety of reasons, it is often necessary to detonate an explosive device deep in a borehole or well, such as an oil well, and the detonation must, of course, be effected remotely and safely. A common technique for actuating such devices utilizes a non-electrical wire or line to the surface, which is pulled to actuate the device, often by means of some type of plunger mechanism to close a switch and thereby fire the explosive. Some devices employing this technique include a hydraulic safety mechanism which necessitates a long, steady pull on the actuating line to actuate the device. Another technique makes use of one or more time-delay mechanisms to allow time for placement of the explosive.
Inventors and engineers working with devices of the same general type as the present invention have long striven to improve the safety of operation of the devices. An underground explosive charge to be detonated in a borehole usually must be accurately positioned. If it has to be repositioned, or totally removed, or if there is a malfunction of the mechanism, it is absolutely essential that the device can be repositioned, or removed from the borehole and disarmed, if desired, without accidental firing of the explosive charge. Detonator devices of this type available heretofore are deficient in many respects relating to safety of operation. Those that rely solely on mechanical actuation may not be repositioned or removed from a borehole without substantial risk of premature explosion. Similarly, those that employ time-delay mechanisms to provide time to properly position the explosive charge do not provide for safe removal and disarming in the event of a malfunction or a change in plans.
In some instances, it may be necessary to place an explosive charge at a certain distance below the surface level of water or oil in a borehole; yet the precise depth of the liquid surface level in the borehole may not be known, or may be changing. It is highly desirable, therefore, to provide some automatic means for arming the detonator apparatus only when it is positioned at the desired depth.
It will be apparent that there has long been a need for a detonator device which satisfies the foregoing requirements relating to safety and convenience of operation. The present invention satisfies this need.